IT IS THE VASCULAR SMOOTH MUSCLE RELAXATION. DILATATION OF THE POSTCAPILLARY VESSELE, INCLUDING LARGE VEINS, PROMOTES PERIPHERAL POOLING OF BLOOD AND DECREASES VENOUS RETURN TO THE HEART, REDUCING LEFT VENTRICULAR END-DIASTOLIC PRESSURE. IT IS ALSO DILATES, LARGE EPICARDIAL CORONARY ARTERIES, HOWEVER, THE EXTENT TO WHICH THIS EFFECT CONTRIBUTES TO THE RELIEF OF EXERTIONAL ANGINA IS UNCLEAR.